This invention relates generally to fasteners and more particularly concerns aircraft type fasteners having interference fit with a work member or members. It basically concerns positive connection of structural members as distinguished from riveted connection of thin skins.
Flush type fastener heads normally are conical in shape to be received in countersunk recesses in the work. There is a continuing problem of tension fatigue in the work surrounding such heads. Repeated bending of the work, as in aircraft structures, produces alternating tension loading of the work panel. The formation of countersinks reduces the straight bore surface areas and the strength of the work panel. Also the reduced non-uniform area of contact of the head against the countersink creates uneven annular clampup, inducing fretting. Another problem results from the use of plated interference fasteners, as for example cadmium plating. It is found that the plate tends to shear off upon engagement with the annular corner or edge between the countersink and straight bore surfaces of the work. The removed material then gathers under the head to block full seating of the head against the countersink surface of the work, resulting in corrosion when fluid enters the gap to reach the fastener surface from which plate has been removed. While various expedients have been resorted to in efforts to alleviate these problems, none of these efforts have provided the unusual advantages in design simplicity, mode of operation and results as are now afforded by the present invention.